The invention relates to a method for the hydraulic conveying of solids and to an apparatus for carrying out this method.
Hydraulic conveying of solids is known, for example, in coal mining, where the coal is introduced into pipes filled with pressurized water and thus brought to the surface.
A considerable problem in the hydraulic conveying of solids arises from the difficulty of finding suitable pumps, which increases with the particle size and concentration of the solid material and with the conveying pressure required. The higher the required conveying pressure, the more uncontrollable will be the wear on the pumps when the solid material which is to be conveyed is fed to the pumps.
In hydraulic conveying plants, for example those having so-called tubular chamber chargers, use is therefore made of arrangements enabling certain amounts of the hydraulic conveying flow to be prepared in the form of a suspension of solids in pipe loops, so-called tubular chambers, and then to be injected into the conveying pipe through the timed opening and closing of valves. High-pressure pumps and solid materials are thus separated.
In this method it is however a disadvantage that the solid material is deposited in the tubular chambers as soon as the conveying is interrupted by the closing of the valves. In comparison with the actual conveying process, higher conveying speeds are needed to whirl up the deposited material again, and this is synonymous with greater energy requirements and consequently once again greater wear on the pipes. Moreover, a method of this kind leads to irregular loading of the suspension with solid material, both as regards the total amount of solid material and as regards the mass of the solid material particles. This in turn means a reduction of the effectiveness of the conveying operation.
In addition, another great disadvantage is the use of valves in the tubular chargers, which requires considerable expenditure for control for operating the valves, which in addition are subject to considerable wear.
In any case, the tubular chamber method is limited in its utilizability, for example in the conveying of a mixture of solid materials having different relative densities, particularly when the latter vary relatively substantially. In such cases, in fact, the solid materials having the higher relative density are deposited in the tubular chamber charger and are whirled up again by the current of conveying medium only at a particularly high speed, so that, for reasons of energy consumption and wear, hydraulic conveying becomes uneconomic.
The problem underlying the invention is therefore that of proposing a method of the kind first defined above and which is exempt from the above described disadvantages of known apparatus and known methods, or at least is substantially less subject to these disadvantages, so that the advantage is gained that hydraulic conveying can be applied to all solid materials and mixtures of solid materials by the use of simple apparatus.
According to the invention this problem is solved in that solid material, the particle size of which is suitable for conveying, is first mixed with liquid only to such an extent that a viscous material of high consistency is obtained, and this viscous material is then injected into the hydraulic conveying medium, which is free of solids.
In this method therefore a highly concentrated suspension is first produced, and it is then injected under favorable conditions of pressure and flow into the actual conveying medium which is free of solids and which is flowing at a suitably high speed. The conveying medium is obviously here predominantly water. The viscous material or suspension containing a high concentration of solid material is conveyed by means known per se, for example piston pumps, while the actual conveying medium free of solids provides the necessary pressure and the necessary speed of flow with the aid of high-pressure centrifugal pumps.
The viscous matieral is injected into the actual conveying pipe containing the liquid free from solids under favorable conditions of pressure and flow.
In the method according to the invention the solid material is therefore injected or introduced into the conveying process only downstream of the high-pressure pumps. The solid material consequently does not come into contact with the high-pressure pumps for the hydraulic conveying medium, so that it cannot give rise to wear. Through the use of a highly concentrated suspension, accurate metering of the amount of solid material, such as is necessary for optimum performance of the hydraulic conveying, is possible and the high pressures required can also be obtained with the aid of ordinary commercially available piston pumps.
The injection of the solid material into the hydraulic conveying medium pipe results in uniform distribution of the solid material particles in the medium and in an acceleration to the conveying speed, because the conveying medium has a turbulent flow, so that whirling and distribution of the particles of solid material are achieved automatically. The acceleration of the injected solid material to conveying speed thus constitutes no problem.
Differentiation of the slip of particles of solid materials of different realtive densities in relation to the conveying speed also does not lead to segregation. In cases of unfavorable mixing and acceleration, variations of the speed of flow and additional turbulence in the conveying current can be achieved by varying the cross-sections of the conveying pipe, so that activated acceleration and mixing of the medium and the solid material occur. Particularly in the case of non-vertical hydraulic conveying and of a conveying speed near the critical suspension speed when the suspension is of low viscosity, these measures according to the invention are surprisingly advantageous.
Thus, in pursuance of the principle of the invention, the conveying pipe may be waisted at the point where the viscous material is injected, so that the speed of flow will be raised and thus the entraining and whirling effect will be increased. In addition, at a higher speed the static pressure will fall in the region of the waisting or constriction, so that the required elevated pressure at which the viscous material is injected, can be lowered.
A constriction of this kind in the conveying pipe may also be abruptly followed by a widening of the cross-section, so that additional turbulence is obtained. In the zone following this widening in the pipe, which is then narrowed again to the diameter of the conveying pipe, an increase of the conveying speed favorable to flow then takes place. The column of solid material being conveyed in the pipe supplying the viscous material acts, when conveying is stopped in the case of vertical conveying, as a plug sealing against the conveying medium under pressure in the main conveying pipe.
The method according to the invention is of particular interest when applied under mining conditions, because it may then be important to use the conveying of viscous material not only for direct charging of solid material into the conveying medium, but also, in extensive, ramified mine workings, for supplying material comminuted to conveying size from various decentralized points to a central charging point of the hydraulic conveying system, in the form of viscous material, even over long distances.